Three-dimensional nonvolatile memory and related read method designed to reduce read disturbance

ABSTRACT

A nonvolatile memory device performs a read operation comprising first and second intervals. In the first interval the device applies a turn-on voltage to string selection lines and ground selection lines connected to the string selection transistors and the ground selection transistors, respectively. In the second interval, the device applies a turn-off voltage to unselected string selection lines and unselected ground selection lines while continuing to apply the turn-on voltage to a selected string selection line and a selected ground selection line. In both the first and second intervals, the device applies a first read voltage to a selected wordline connected to memory cells to be read by the read operation and applying a second read voltage to unselected wordlines among connected to memory cells not to be read by the read operation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a Continuation of U.S. application Ser. No. 15/203,826, filedJul. 7, 2016, which is a Continuation of U.S. application Ser. No.14/880,820, filed Oct. 12, 2015, issued a U.S. Pat. No. 9,418,749 onAug. 16, 2016, which is a Continuation of U.S. application Ser. No.14/153,164, filed Jan. 13, 2014, issued as U.S. Pat. No. 9,190,151 onNov. 17, 2015, which claims priority under 35 U.S.C. § 119 to KoreanPatent Application No. 10-2013-0022313 filed Feb. 28, 2013, the subjectmatter of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

The inventive concept relates generally to semiconductor memory devices,and more particularly, to nonvolatile memory devices and related methodsfor performing read operations with reduced read disturbance.

Semiconductor memory devices can be roughly divided into two categoriesaccording to whether they retain stored data when disconnected frompower. These categories include volatile memory devices, which losestored data when disconnected from power, and nonvolatile memorydevices, which retain stored data when disconnected from power.

Examples of volatile memory devices include static random access memory(SRAM) devices, dynamic random access memory (DRAM) devices, andsynchronous DRAM (SDRAM) devices. Examples of nonvolatile memory devicesinclude flash memory devices, read only memory (ROM) devices,programmable ROM (PROM) devices, electrically erasable and programmableROM (EEPROM) devices, and various forms of resistive memory such asphase-change RAM (PRAM), ferroelectric RAM (FRAM), and resistive RAM(RRAM).

In recent years, researchers have developed three-dimensional (3D)semiconductor memory devices in an effort to increase the integrationdensity of semiconductor memory devices. Structural characteristics of3D semiconductor memory devices are different from those oftwo-dimensional (2D) semiconductor memory devices, so they requiredifferent driving methods compared to the 2D semiconductor memorydevices. For example, due to their different structural characteristics,the 3D semiconductor memory devices may experience different electricalparasitics, which may require driving voltages to be provided withdifferent levels and timing compared to 2D semiconductor memory devices.

SUMMARY OF THE INVENTION

In one embodiment of the inventive concept, a method is provide forperforming a read operation in a nonvolatile memory comprising multiplecell strings each comprising multiple memory cells stacked in adirection perpendicular to a substrate, a ground selection transistordisposed between the memory cells and the substrate, and a stringselection transistor disposed between the memory cells and a bitline.During a first interval, the method applies a first turn-on voltage tostring selection lines connected to string selection transistors of afirst group of cell strings among the multiple cell strings, and to afirst ground selection line connected in common to ground selectiontransistors of the first group of cell strings, and applies a secondturn-on voltage to string selection lines connected to string selectiontransistors of a second group of cell strings among the multiple cellstrings, and to a second ground selection line connected in common toground selection transistors of the second group of cell strings. Duringa second interval following the first interval, the method applies thefirst turn-on voltage to a string selection line of a selected cellstring among the first group of cell strings, and to the first groundselection line, and applies a turn-off voltage to string selection linesof unselected cell strings among the first group of cell strings, tostring selection lines of cell strings in the second group of cellstrings, and to the second ground selection line. During both the firstand second intervals, the method applies a first read voltage to aselected wordline among wordlines connected to memory cells of the firstgroup of cell strings and the second group of cell strings, and appliesa second read voltage to unselected wordlines among the wordlinesconnected to memory cells of the first group of cell strings and thesecond group of cell strings of the wordlines.

In another embodiment of the inventive concept, a nonvolatile memorycomprises a memory cell array comprising multiple cell strings each cellstring comprising multiple memory cells stacked in a directionperpendicular to a substrate, a ground selection transistor disposedbetween the memory cells and the substrate, and a string selectiontransistor disposed between the memory cells and a bitline, an addressdecoder connected to multiple memory cells of the cell strings throughwordlines, to string selection transistors of the cell strings throughstring selection lines, and to ground selection transistors of the cellstrings through ground selection lines, and a read/write circuitconnected to string selection transistors of the cell strings throughbitlines. In a read operation, the address decoder applies a turn-onvoltage to string selection lines and ground selection lines connectedto the string selection transistors and ground selection transistors,respectively, and then applies a turn-off voltage to unselected stringselection lines and unselected ground selection lines among the stringselection lines and ground selection lines while continuing to apply theturn-on voltage to a selected string selection line and a selectedground selection line among the string selection lines and groundselection lines.

In another embodiment of the inventive concept, a method is provided forperforming a read operation in a nonvolatile memory comprising multiplecell strings each comprising multiple memory cells stacked in adirection perpendicular to a substrate, a ground selection transistordisposed between the memory cells and the substrate, and a stringselection transistor disposed between the memory cells and a bitline. Ina first interval of the read operation, the method applies a turn-onvoltage to string selection lines and ground selection lines connectedto the string selection transistors and the ground selectiontransistors, respectively. In a second interval following the firstinterval, the method applies a turn-off voltage to unselected stringselection lines and unselected ground selection lines among the stringselection lines and ground selection lines while continuing to apply theturn-on voltage to a selected string selection line and a selectedground selection line among the string selection lines and groundselection lines. In both the first and second intervals, the methodapplies a first read voltage to a selected wordline connected to memorycells to be read by the read operation and applying a second readvoltage to unselected wordlines among connected to memory cells not tobe read by the read operation.

These and other embodiments of the inventive concept can potentiallyreduce read disturbances by turning on various string and groundselection transistors in a predetermined order and with predeterminedlevels such that boosted charges are discharged through the string andground selection transistors and a potential distribution in differentcell strings becomes substantially uniform.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate selected embodiments of the inventive concept.In the drawings, like reference numbers indicate like features.

FIG. 1 is a block diagram of a nonvolatile memory device according to anembodiment of the inventive concept.

FIG. 2 is a circuit diagram of a memory block according to an embodimentof the inventive concept.

FIG. 3 is a flowchart illustrating a method of performing a readoperation in a nonvolatile memory according to an embodiment of theinventive concept.

FIGS. 4 and 5 are diagrams illustrating a first example of voltages thatcan be used in the method of FIG. 3.

FIG. 6 is a timing diagram of an example read operation using thevoltages illustrated in FIGS. 4 and 5.

FIG. 7 is a diagram of a channel voltage of a cell string CS31 when aread operation is performed using the voltages illustrated in FIGS. 4 to6.

FIG. 8 is a diagram of a channel voltage of a cell string CS21 when aread operation is performed using the voltages illustrated in FIGS. 4 to6.

FIG. 9 is a diagram of a second example of voltages that can be used inthe method of FIG. 3.

FIG. 10 is a timing diagram of an example read operation using thevoltages illustrated in FIGS. 5 and 9.

FIG. 11 is a diagram of a third example of voltages that can be used inthe method of FIG. 3.

FIG. 12 is a timing diagram of an example read operation using thevoltages illustrated in FIGS. 5 and 11.

FIG. 13 is a diagram of a fourth example of voltages that can be used inthe method of FIG. 3.

FIG. 14 is a timing diagram of an example read operation using thevoltages illustrated in FIGS. 5 and 13.

FIG. 15 is a diagram of a fifth example of voltages that can be used inthe method of FIG. 3.

FIG. 16 is a timing diagram of an example read operation using thevoltages illustrated in FIGS. 5 and 15.

FIG. 17 is a diagram of a sixth example of voltages that can be used inthe method of FIG. 3.

FIG. 18 is a timing diagram of an example read operation using thevoltages illustrated in FIGS. 5 and 17.

FIG. 19 is a circuit diagram of a memory block according to anembodiment of the inventive concept.

FIG. 20 is a block diagram of a memory system according to an embodimentof inventive concepts.

FIG. 21 is a block diagram of a memory system according to an embodimentof the inventive concept.

FIG. 22 is a diagram of a memory card according to an embodiment of theinventive concept.

FIG. 23 is a diagram of a solid state drive (SSD) according to anembodiment of the inventive concept.

FIG. 24 is a block diagram of a computing device according to anembodiment of the inventive concept.

DETAILED DESCRIPTION

Embodiments of the inventive concept are described below with referenceto the accompanying drawings. These embodiments are presented asteaching examples and should not be construed to limit the scope of theinventive concept.

In the description that follows, the terms “first”, “second”, “third”,etc., may be used to describe various features, but these featuresshould not be limited by these terms. Rather, these terms are usedmerely to distinguish between different features. Thus, a first featurecould be termed a second feature without departing from the teachings ofthe inventive concept.

Spatially relative terms, such as “beneath”, “below”, “lower”, “under”,“above”, “upper” and the like, may be used for ease of description todescribe one feature's relationship to another feature(s) as illustratedin the figures. The spatially relative terms are intended to encompassdifferent orientations of the device in use or operation in addition tothe orientation depicted in the figures. For example, if the device inthe figures is turned over, elements described as “below” or “beneath”or “under” other elements or features would then be oriented “above” theother elements or features. Thus, the terms “below” and “under” canencompass both an orientation of above and below. The device may beotherwise oriented (rotated 90 degrees or at other orientations) and thespatially relative descriptors used herein interpreted accordingly. Inaddition, it will also be understood that where a layer is referred toas being “between” two layers, it can be the only layer between the twolayers, or one or more intervening layers may also be present.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the inventiveconcept. As used herein, the singular forms “a”, “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. Terms such as “comprises” and/or “comprising,”where used in this specification, indicate the presence of statedfeatures but do not preclude the presence or addition of one or moreother features. As used herein, the term “and/or” includes any and allcombinations of one or more of the associated listed items.

Where a feature is referred to as being “on”, “connected to”, “coupledto”, or “adjacent to” another feature, it can be directly on, connected,coupled, or adjacent to the other feature, or intervening features maybe present. In contrast, where a feature is referred to as being“directly on,” “directly connected to”, “directly coupled to”, or“immediately adjacent to” another feature, there are no interveningfeatures present.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art. Terms such as those defined in commonlyused dictionaries should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art and/orthe present specification and will not be interpreted in an idealized oroverly formal sense unless expressly so defined herein.

The term “selected memory block” denotes a memory block selected forprogramming, erasing, or reading, from among multiple memory blocks. Theterm “selected sub block” denotes a sub block selected for programming,erasing, or reading, from among multiple sub blocks in one memory block.

The term “selected bitline” or “selected bitlines” denotes a bitline orbitlines connected to a cell transistor to be programmed or read, fromamong multiple bitlines. The term “unselected bitline” or “unselectedbitlines” denotes a bitline or bitlines connected to a cell transistorto be program-inhibited or read-inhibited, from among multiple bitlines.

The term “selected string selection line” denotes a string selectionline connected to a cell string including a cell transistor to beprogrammed or read, from among multiple string selection lines. The term“unselected string selection line” or “unselected string selectionlines” denotes a remaining string selection line or remaining stringselection lines other than the selected string selection line from amongmultiple string selection lines. The term “selected string selectiontransistors” denotes string selection transistors connected to aselected string selection line. The term “unselected string selectiontransistors” denotes string selection transistors connected to anunselected string selection line or unselected string selection lines.

The term “selected ground selection line” denotes a ground selectionline connected to a cell string including a cell transistor to beprogrammed or read, among multiple ground selection lines. The term“unselected ground selection line” denotes a remaining ground selectionline or remaining ground selection lines other than the selected groundselection line from among multiple ground selection lines. The term“selected ground selection transistors” denotes ground selectiontransistors connected to a selected ground selection line. The term“unselected ground selection transistors” denotes ground selectiontransistors connected to an unselected ground selection line orunselected ground selection lines.

The term “unselected wordline” denotes a wordline, connected to a celltransistor to be programmed or read, from among multiple wordlines. Theterm “unselected wordline” or “unselected wordlines” denotes a remainingwordlines or remaining wordlines other than a selected wordline fromamong multiple wordlines.

The term “selected memory cell” or “selected memory cells” denotesmemory cells to be programmed or read among multiple memory cells. Theterm “unselected memory cell” or “unselected memory cells” denotes aremaining memory cell or remaining memory cells other than a selectedmemory cell or selected memory cells from among multiple memory cells.

Embodiments of the inventive concept will be described with reference toa NAND flash memory. However, the inventive concept is not limitedthereto. For example, the inventive concept may also be applied tononvolatile memory devices such as an EEPROM, a NOR flash memory, PRAM,a Magnetic RAM (MRAM), RRAM, an FRAM, and the like.

FIG. 1 is a block diagram of a nonvolatile memory device 100 accordingto an embodiment of the inventive concept.

Referring to FIG. 1, nonvolatile memory device 100 comprises a memorycell array 110, an address decoder 120, a read/write circuit 130, andcontrol logic and voltage generator block 140.

Memory cell array 110 is connected to address decoder 120 throughwordlines WL, string select lines SSL, and ground selection lines GSLand to read/write circuit 130 through bitlines BL. Memory cell array 110comprises multiple memory blocks BLK1 to BLKz, each of which multiplememory cells and multiple selection transistors. The memory cells areconnected to the wordlines, and the selection transistors are connectedto string select lines SSL or ground selection lines GSL. The memorycells of each memory block are stacked in a direction perpendicular to asubstrate to form a 3D structure. Each memory cell stores one or morebits.

Address decoder 120 is connected to memory cell array 110 throughwordlines WL, string select lines SSL, and ground selection lines GSL.Address decoder 120 operates under control of control logic and voltagegenerator block 140. Address decoder 120 receives an address ADDR froman external device.

Address decoder 120 is configured to decode a row address of thereceived address ADDR. Address decoder 120 selects wordlines WL, stringselect lines SSL, and ground selection lines GSL based on the decodedrow address. Address decoder 120 receives various voltages from controllogic and voltage generator block 140 and transfers the receivedvoltages to selected and unselected string selection lines SSL,wordlines WL and ground selection lines GSL.

Address decoder 120 is configured to decode a column address of thereceived address ADDR. Address decoder 120 transfers decoded columnaddress DCA to read/write circuit 130. For example, address decoder 120may comprise features such as a row decoder, a column address, anaddress buffer, and so on.

Read/write circuit 130 is connected to memory cell array 110 throughbitlines BL, and it exchanges data with the external device. Read/writecircuit 130 operates under control of control logic and voltagegenerator block 140. Read/write circuit 130 receives decoded columnaddress DCA from address decoder 120, and it selects bitlines BL usingthe decoded column address.

Read/write circuit 130 receives data from the external device, and itwrites the received data at memory cell array 110. Read/write circuit130 reads data from memory cell array 110 and transfers the read data tothe external device. Read/write circuit 130 reads data from a firststorage region of memory cell array 110 and writes the read data to asecond storage region of memory cell array 110. For instance, read/writecircuit 130 may perform a copy-back operation.

Read/write circuit 130 typically comprises features such as a pagebuffer (or, page register), a column selection circuit, a data buffer,and so on. In some embodiments, read/write circuit 130 may also includefeatures such as a sense amplifier, a write driver, a column selectioncircuit, a data buffer, and so on.

Control logic and voltage generator block 140 is connected to addressdecoder 120 and read/write circuit 130. Control logic and voltagegenerator block 140 is configured to control operations of nonvolatilememory device 100. Control logic and voltage generator block 140 isgenerally configured to generate various voltages used by nonvolatilememory device 100. Control logic and voltage generator block 140operates in response to a control signal CTRL and a command CMDtransferred from the external device.

FIG. 2 is a circuit diagram of a memory block BLKa according to anembodiment of the inventive concept. Memory block BLKa is arepresentative example of one of memory blocks BLK1 to BLKz of memorycell array 110 of FIG. 1.

Referring to FIGS. 1 and 2, memory block BLKa comprises multiple cellstrings CS11 to CS41 and CS12 to CS42. Cell strings CS11 to CS41 andCS12 to CS42 are arranged along a row direction and a column directionand form rows and columns.

Each of cell strings CS11 to CS41 and CS12 to CS42 comprises a groundselection transistor GST, memory cells MC1 to MC6, and a stringselection transistor SST. In each of cell strings CS11 to CS41 and CS12to CS42, ground selection transistor GST, memory cells MC1 to MC6, andstring selection transistor SST may be stacked in a height directionperpendicular to a substrate.

Rows of cell strings CS11 to CS41 and CS12 to CS42 are connected todifferent string selection lines SSL1 to SSL4, respectively. Forexample, string selection transistors SST in cell strings CS11 and CS12are connected in common to string selection line SSL1, and stringselection transistors SST in cell strings CS21 and CS22 are connected incommon to string selection line SSL2. String selection transistors SSTin cell strings CS31 and CS32 are connected in common to stringselection line SSL3, and string selection transistors SST in cellstrings CS41 and CS42 are connected in common to string selection lineSSL4.

Columns of cell strings CS11 to CS41 and CS12 to CS42 are connected todifferent bitlines BL1 and BL2, respectively. For example, stringselection transistors SST in cell strings CS11 to CS41 are connected incommon to bitline BL1, and string selection transistors SST in cellstrings CS12 to CS42 are connected in common to bitline BL2.

At least two rows of cell strings are connected in common to a groundselection line, and cell strings CS11 to CS41 and CS12 to CS42 areconnected to at least two different ground selection lines GSL1 andGSL2. For example, ground selection transistors GST of cell stringsCS11, CS21, CS12, and CS22 are connected in common to ground selectionline GSL1, and ground selection transistors GST of cell strings CS31,CS41, CS32, and CS42 are connected in common to ground selection lineGSL2.

Memory cells at the same height from a substrate (or, ground selectiontransistors GST) are connected in common to a wordline, and memory cellsat different heights are connected to different wordlines. For example,memory cells MC1 are connected in common to a wordline WL1, and memorycells MC2 are connected in common to a wordline WL2. Memory cells MC3are connected in common to a wordline WL3, and memory cells MC4 areconnected in common to a wordline WL4. Memory cells MC5 are connected incommon to a wordline WL5, and memory cells MC6 are connected in commonto a wordline WL6. Ground selection transistors GST of cell strings CS11to CS41 and CS12 to CS42 are connected in common to a common source lineCSL.

Memory block BLKa illustrated in FIG. 2 is merely an example, and theinventive concept is not limited to the features of this memory block.For example, the number of rows of cell strings may be increased ordecreased. As the number of rows of cell strings is varied, the numberof string selection lines connected to rows of cell strings and thenumber of cell strings connected to a bitline may be also changed. Asthe number of rows of cell strings is varied, the number of groundselection lines connected to at least two rows of cell strings may bealso changed.

The number of columns of cell strings may be increased or decreased. Asthe number of columns of cell strings is varied, the number of bitlinesconnected to columns of cell strings and the number of cell stringsconnected to a string selection line may be also changed.

The height of cell strings may be increased or decreased. For example,the number of stacked memory cells in each cell string may be increasedor decreased. In this case, the number of wordlines may be also changed.For example, the number of ground or string selection transistors ineach cell string may increase. In this case, the number of ground orstring selection lines may be also changed. If the number of ground orstring selection transistors increases, ground or string selectiontransistors may be stacked substantially the same as such a manner thatthe memory cells are stacked.

In some embodiments, a read operation and a write operation may beperformed by a unit of a row of cell strings. Cell strings CS11 to CS41and CS12 to CS42 may be selected by a two-row unit by ground selectionlines GSL1 and GSL2 and by a row unit by string selection lines SSL1 toSSL4.

In a selected row of cell strings, the read operation and the writeoperation may be performed by a page unit. A page may be a row of memorycells connected to a wordline. In a selected row of cell strings, memorycells may be selected by a page unit by wordlines WL1 to WL6.

FIG. 3 is a flowchart illustrating a read method of a nonvolatile memory100 according to an embodiment of the inventive concept.

Referring to FIGS. 2 and 3, in operation S110, a turn-on voltage isapplied to string selection lines SSL1 and SSL4 and ground selectionlines GSL1 and GSL2. In operation S120, a first read voltage is appliedto a selected wordline, and a second read voltage is applied tounselected wordlines. The first read voltage and the second read voltagemay be simultaneously applied. In operation S130, a turn-off voltage isapplied to unselected string selection lines and unselected groundselection lines.

Various examples of the timing and voltage levels to be used inconnection with operations S110 through S130 will be presented withreference to FIG. 4 through 18 below.

FIGS. 4 and 5 are diagrams illustrating a first example of voltages thatcan be used in the method of FIG. 3. The voltages illustrated in FIG. 4are applied to cell strings CS11 to CS41 in a first interval of a readoperation, and the voltages illustrated in FIG. 5 are applied to cellstrings CS11 to CS41 in a second interval of the read operationfollowing the first interval.

In FIGS. 4 and 5, as well as similar diagrams such as those in FIGS. 9,11, 13, 15, and 17, specific cell strings are labeled along an upperx-axis, and various signal lines are labeled along a left y-axis. Thesignal lines corresponding to those cell strings are written in ageneric form, i.e., SSL rather than SSL1, SSL2, etc.; GSL rather thanGSL1, GSL2, etc.; and so on. Their specific form can be inferred fromFIG. 2 in combination with the relevant cell string labels. Forinstance, cell string CS11 corresponds to string selection line SSL1 andground selection line GSL1, cell string CS41 corresponds to stringselection line SSL4 and ground selection line GSL2, and so on.

Shading is used in FIG. 5 to indicate voltages that change between thefirst and second intervals of FIGS. 4 and 5. Although FIGS. 4 and 5illustrate voltages applied to a first row of cell strings CS11 to CS41,the same voltages is applied to a second row of cell strings CS12 toCS42.

Referring to FIG. 4, cell string CS11 is selected, and cell strings CS21to CS41 are unselected. A turn-on voltage is applied to string selectionlines SSL1 to SSL4 and ground selection lines GSL1 and GSL2. The turn-onvoltage is a voltage for turning on string and ground selectiontransistors SST and GST.

In further detail, a first turn-on voltage VON1 is applied to a selectedground selection line GSL1 connected to the selected cell string CS11,and a second turn-on voltage is applied to an unselected groundselection line GSL2.

First turn-on voltage VON1 is applied to a selected string selectionline SSL1 connected to the selected cell string CS11. First turn-onvoltage VON1 is applied to an unselected string selection line SSL2corresponding to the selected ground selection line GSL1. In otherwords, first turn-on voltage VON1 is applied to both a string selectionline of a selected cell string, as well as a string selection line of anunselected cell string that shares a ground selection line with theselected cell string. Second turn-on voltage VON2 is applied tounselected string selection lines SSL3 and SSL4 corresponding to theunselected ground selection line GSL2.

In the illustrated examples, first turn-on voltage VON1 is a readvoltage VREAD, which is a high voltage. Read voltage VREAD has a levelsufficient to turn on memory cell transistors, string selectiontransistors, or ground selection transistors, regardless of whetherthose transistors are in a programmed state. Second turn-on voltage VON2is a positive voltage VP lower than read voltage VREAD.

A first read voltage VR1 is applied to unselected wordlines. First readvoltage VR1 is also read voltage VREAD. A second read voltage VR1 isapplied to a selected wordline. Second read voltage VR1 is a selectionread voltage VRD for determining program states of memory cells MC1 toMC6. Selection read voltage VRD may have one of various voltage levelsused to determine threshold voltage distributions according to programstates of memory cells MC1 to MC6.

Referring to FIG. 5, a turn-off voltage VOFF is applied to unselectedstring selection lines SSL2 to SSL4 and the unselected ground selectionline GSL2. The turn-off voltage VOFF is a voltage with a levelsufficient to turn off the string and ground selection transistors SSTand GST. For example, the turn-off voltage VOFF may be a ground voltageVSS.

FIG. 6 is a timing diagram of an example read operation using thevoltages illustrated in FIGS. 4 and 5. In FIG. 6, the first interval ofFIG. 4 is between a time T1 and a time T2, and the second interval ofFIG. 5 is after time T2.

Referring to FIG. 6, at time T1, first turn-on voltage VON1 is appliedto selected string selection line SSL1. First turn-on voltage VON1 isalso applied to a first unselected string selection line. The firstunselected string selection line may be an unselected string selectionline SSL2 corresponding to a selected ground selection line GSL1. Secondturn-on voltage VON2 is applied to second unselected string selectionlines. The second unselected string selection lines may be unselectedstring selection lines SSL3 and SSL4 corresponding to unselected groundselection line GSL2.

First read voltage VR1 is applied to an unselected wordline, and secondread voltage VR2 is applied to a selected wordline. For example, secondread voltage VR2 may be ground voltage VSS. First turn-on voltage VON1is applied to the selected ground selection line GSL1, and secondturn-on voltage VON2 is applied to the unselected ground selection lineGSL2.

At time T2, turn-off voltage VOFF is applied to the first unselectedstring selection line SSL2 and second unselected string selection linesSSL3 and SSL4. The turn-off voltage VOFF is applied to the unselectedground selection line GSL2. Voltages of the selected string selectionline SSL1, the selected ground selection line GSL1, the selectedwordline and the unselected wordlines may be maintained between thefirst and second intervals.

FIG. 7 is a diagram of a channel voltage of a cell string CS31 whenvoltages are applied according to FIGS. 4 to 6.

Referring to FIG. 7, a cell string CS31 connected to an unselectedground selection line GSL2 and an unselected string selection line SSL3and a channels voltage of cell string CS31 are illustrated. A horizontalaxis indicates a channel voltage, and a vertical axis indicates aheight. A first line L1 shown in dotted line represents a channelvoltage in a device using a conventional read method, and a second lineL2 shown in solid line represents a channel voltage in a device usingthe voltages of FIGS. 4 to 6.

In the conventional read method, a turn-on voltage is not applied to anunselected ground selection line GSL2 and second unselected stringselection lines SSL3 and SSL4 in a first interval. Thus, a stringselection transistor SST and a ground selection transistor GST in cellstring CS31 maintain a turn-off state. A string channel of cell stringCS31 may be floated.

A first read voltage VR1 is applied to unselected wordlines WL1, WL2,and WL4 to WL6. At this time, coupling is generated between theunselected wordlines WL1, WL2, and WL4 to WL6 and memory cells MC1 toMC6. Voltages of channels of memory cells MC1, MC2, and MC4 to MC6 maybe boosted by the coupling as illustrated by the first line L1.

At a point P1, a potential difference is generated between a bitline BL1and a channel of memory cell MC6. At a point P2, a potential differenceis generated between channels of memory cells MC4 and MC3. At a pointP3, a potential difference is generated between channels of memory cellsMC3 and MC2. At a point P4, a potential difference is generated betweena channel of memory cell MC6 and a common source line CSL.

The potential difference may cause generation of hot electrons at pointsP1 to P4. The hot electrons may be accumulated at memory cells MC1 toMC6, string selection transistor SST or ground selection transistor GST.The accumulated hot electrons may cause variations in threshold voltagesof memory cells MC1 to MC6, a threshold voltage of string selectiontransistor SST or a threshold voltage of ground selection transistorGST. That is, potential differences at points P1 to P4 may cause readdisturbances.

According to an embodiment of the inventive concept, second turn-onvoltage VON2 is applied to the second unselected string selection linesSSL3 and SSL4 and the unselected ground selection line GSL2 at the sametime when first read voltage VR1 is applied to the unselected wordlinesWL1, WL2, and WL4 to WL6. If second turn-on voltage VON2 is applied,string selection transistor SST and ground selection transistor GST maybe turned on.

A channel voltage corresponding to memory cells MC4 to MC6 is dischargedto bitline BL1 through string selection transistor SST. A channelvoltage corresponding to memory cells MC1 and MC2 is discharged tocommon source line CSL through ground selection transistor GST. Thus,channel voltages of memory cells MC1, MC2, and MC4 to MC6 connected tothe unselected wordlines WL1, WL2, and WL4 to WL6 may be lowered, sothat read disturbance is prevented or reduced.

Also, voltages applied to the second unselected string selection linesSSL3 and SSL4 and the unselected ground selection line GSL2 may be equalto second turn-on voltage VON2. A channel voltage corresponding tomemory cells MC1 and MC2 and a channel voltage corresponding to memorycells MC4 to MC6 may be leveled. If channel voltages at both sides of amemory cell MC3 connected to a selected wordline WL3 are leveled, theprobability that hot electrons are generated at memory cell MC3 may bereduced. Thus, read disturbance may be prevented or reduced.

FIG. 8 is a diagram of a channel voltage of a cell string CS21 whenvoltages are applied according to FIGS. 4 to 6.

In FIG. 8, a cell string CS21 connected to a selected ground selectionline GSL1 and an unselected string selection line SSL2 and a channelsvoltage of cell string CS31 are illustrated. In FIG. 8, a horizontalaxis indicates a channel voltage, and a vertical axis indicates aheight. In FIG. 7, a first line L1 shown in dotted line shows a channelvoltage of a conventional read method, and a second line L2 shown insolid line shows a channel voltage produced by the voltages of FIGS. 4to 6.

In the conventional read method, a turn-on voltage is not applied to theselected ground selection line GSL1, and is not be applied to theunselected string selection line SSL2. Thus, a string selectiontransistor SST in cell string CS21 maintains a turn-off state, and aground selection transistor GST in cell string CS21 is turned on.

As a first read voltage VR1 is applied to unselected wordlines WL1 andWL2, channels of memory cells MC1 and MC2 are connected to a commonsource line CSL through a ground selection transistor GST. Because asecond read voltage VR2 is applied to a selected wordline WL3, channelsof memory cells MC4 to MC6 may be floated. Channel voltages of memorycells MC4 to MC6 may be boosted by first read voltage VR1 applied towordlines WL4 to WL6.

Thus, as shown in first line L1, channel voltages of memory cells MC1 toMC2 may be discharged to a common source line CSL to maintain a lowvoltage. Channel voltages of memory cells MC4 to MC6 may be boosted.

At point P1, a potential difference is generated between a bitline BL1and a channel of memory cell MC6. At point P2, a potential difference isgenerated between channels of memory cells MC4 and MC3.

The potential differences existing at points P1 and P2 may causegeneration of hot electrons. The hot electrons may be accumulated atmemory cells MC1 to MC6, string selection transistor SST or groundselection transistor GST. The accumulated hot electrons may cause avariation in threshold voltages of memory cells MC1 to MC6, a thresholdvoltage of string selection transistor SST or a threshold voltage ofground selection transistor GST. That is, potential differencesgenerated at points P1 and P2 causes read disturbances.

According to an embodiment of the inventive concept, first turn-onvoltage VON1 is applied to the unselected string selection line SSL1 atthe same time when first read voltage VR1 is applied to the unselectedwordlines WL1, WL2, and WL4 to WL6 and first turn-on voltage VON1 isapplied to the unselected string selection line SSL1. If first turn-onvoltage VON1 is applied, string selection transistor SST and groundselection transistor GST may be turned on.

A channel voltage corresponding to memory cells MC4 to MC6 is dischargedto bitline BL1 through string selection transistor SST. Thus, channelvoltages of memory cells MC4 to MC6 connected to the unselectedwordlines WL4 to WL6 may be lowered, so that read disturbance isprevented or reduced.

Also, voltages applied to the unselected string selection line SSL1 andthe selected ground selection line GSL1 may be equal to first turn-onvoltage VON1. Thus, a channel voltage corresponding to memory cells MC1and MC2 and a channel voltage corresponding to memory cells MC4 to MC6may be leveled. If channel voltages at both sides of a memory cell MC3connected to a selected wordline WL3 are leveled, the probability thathot electrons are generated at memory cell MC3 may be reduced. Thus,read disturbance may be prevented or reduced.

FIG. 9 is a diagram of a second example of voltages that can be used inthe method of FIG. 3. Compared to FIG. 4, first turn-on voltage VON1 isapplied to string selection lines SSL1 to SSL4 and ground selectionlines GSL1 and GSL2. Afterwards, as illustrated in FIG. 5, a turn-offvoltage VOFF is applied to unselected string selection lines SSL2 toSSL4 and an unselected ground selection line GSL2.

FIG. 10 is a timing diagram of an example read operation using thevoltages illustrated in FIGS. 5 and 9.

Referring to FIGS. 1 to 3, 5, 9 and 10, at time T1, first turn-onvoltage VON1 is applied to a selected string selection line SSL1. Firstturn-on voltage VON1 is applied to a first unselected string selectionline. First turn-on voltage VON1 is applied to second unselected stringselection lines.

A first read voltage VR1 is applied to an unselected wordline, and asecond read voltage VR2 is applied to a selected wordline. First turn-onvoltage VON1 is applied to a selected ground selection line GSL1. Secondturn-on voltage VON2 is applied to an unselected ground selection lineGSL2.

At time T2, an additional operation is performed before voltages of theunselected ground selection line GSL2 and the second unselected stringselection lines SSL3 and SSL4 reach a target level of first turn-onvoltage VON1. At time T2, turn-off voltage VOFF is applied to theunselected ground selection line GSL2 and the second unselected stringselection lines SSL3 and SSL4.

At time T3, an additional operation is performed before a voltage of thefirst unselected string selection line SSL2 reaches a target level offirst turn-on voltage VON1. At time T3, turn-off voltage VOFF is appliedto the first unselected string selection line SSL2.

That is, the same voltage is applied to string selection lines SSL1 toSSL4 and ground selection lines GSL1 and GSL2, and the turn-off voltageis applied before voltages of the unselected ground selection line GSL2and the second unselected string selection lines SSL3 and SSL4 reach atarget level. Thus, the same operation as that described with referenceto FIGS. 4 to 6 may be performed.

FIG. 11 is a diagram of a third example of voltages that can be used inthe method of FIG. 3. Compared to FIG. 4, a third turn-on voltage VON3is applied to a selected wordline. The third turn-on voltage VON3 may bea positive voltage VP. The third turn-on voltage VON3 can be set to belower than a read voltage VREAD. Afterwards, as illustrated in FIG. 5,turn-off voltage VOFF is applied to the selected wordline.

FIG. 12 is a timing diagram of an example read operation using thevoltages illustrated in FIGS. 5 and 11.

Referring to FIGS. 1 to 3, 5, 11 and 12, at time T1, first turn-onvoltage VON1 is applied to a selected string selection line SSL1. Firstturn-on voltage VON1 is applied to a first unselected string selectionline. First turn-on voltage VON1 is applied to a second unselectedstring selection lines.

A first read voltage VR1 is applied to an unselected wordline, and athird read voltage VR3 is applied to a selected wordline. First turn-onvoltage VON1 is applied to a selected ground selection line GSL1. Firstturn-on voltage VON1 is applied to an unselected ground selection lineGSL2.

At time T2, turn-off voltage VOFF is applied to a first unselectedstring selection line SSL2 and to second unselected string selectionlines SSL3 and SSL4. The turn-off voltage VOFF is applied to anunselected ground selection line GSL2. A second read voltage VR2 isapplied to a selected wordline.

In embodiments described with reference to FIGS. 5, 11 and 12, after thethird turn-on voltage VON3 is applied to a selected wordline, secondread voltage VR2 is applied. When the third turn-on voltage is applied,memory cells connected to the selected wordline may be turned on.

As described with reference to FIGS. 7 and 8, when second read voltageVR2 is applied to a selected wordline, memory cells connected to theselected wordline may be turned off. At this time, a string channel maybe divided into two portions on the basis of the selected wordline.

According to an embodiment of the inventive concept, the third turn-onvoltage VON3 is applied to a selected wordline, and then second readvoltage VR2 is applied thereto. Thus, channel voltages of memory cellsmay be leveled before a string channel is divided into two portions bysecond read voltage VR2. Because channel voltages of memory cells ineach cell string are leveled on the basis of a selected memory cell, theprobability that hot electrons are generated at the selected memory cellmay be suppressed. That is, read disturbance may be further prevented orreduced.

FIG. 13 is a diagram of a fourth example of voltages that can be used inthe method of FIG. 3. Compared to FIG. 9, first turn-on voltage VON1 isapplied to a selected wordline. The first turn-on voltage may be a readvoltage VREAD. Afterwards, as illustrated in FIG. 5, a turn-off voltageis applied to the selected wordline.

FIG. 14 is a timing diagram of an example read operation using thevoltages illustrated in FIGS. 5 and 13.

Referring to FIGS. 1 to 3, 5, 13 and 14, at time T1, first turn-onvoltage VON1 is applied to a selected string selection line SSL1. Firstturn-on voltage VON1 is applied to a first unselected string selectionline. First turn-on voltage VON1 is applied second unselected stringselection lines.

A first read voltage VR1 is applied to an unselected wordline, and firstturn-on voltage VON1 is applied to a selected wordline. First turn-onvoltage VON1 is applied to a selected ground selection line GSL1. Firstturn-on voltage VON1 is applied to an unselected ground selection lineGSL2.

At time T2, an additional operation may be performed before voltages ofthe unselected ground selection line GSL2 and second unselected stringselection lines SSL3 and SSL4 reach a target level of first turn-onvoltage VON1. At time T2, turn-off voltage VOFF is applied to theunselected ground selection line GSL2 and the second unselected stringselection lines SSL3 and SSL4. A second read voltage VR2 is applied tothe selected wordline.

At time T3, an additional operation may be performed before a voltage ofthe first unselected string selection line SSL2 reaches a target levelof first turn-on voltage VON1. At time T3, turn-off voltage VOFF isapplied to the first unselected string selection line SSL2.

FIG. 15 is a diagram of a fifth example of voltages that can be used inthe method of FIG. 3. Compared to FIG. 4, second turn-on voltage VON2 isapplied to all string selection lines SSL, unselected wordlines and allground selection lines GSL. Afterwards, as illustrated in FIG. 5, firstturn-on voltage VON1 is applied to a selected string selection line, afirst read voltage VR1 is applied to the unselected wordlines, andturn-off voltage VOFF is applied to an unselected ground selection lineGSL.

FIG. 16 is a timing diagram of an example read operation using thevoltages illustrated in FIGS. 5 and 15.

Referring to FIGS. 1 to 3, 5, 15 and 16, at time T1, second turn-onvoltage VON2 is applied to a selected string selection line SSL1, afirst unselected string selection line SSL2, a second unselected stringselection line SSL3 or SSL4, unselected wordlines, a selected groundselection line GSL1, and an unselected ground selection line GSL2.

After voltages of the second unselected string selection line SSL3 orSSL4 and the unselected ground selection line GSL2 reach second turn-onvoltage VON2, at time T2, turn-off voltage VOFF is applied to the secondunselected string selection line SSL3 or SSL4 and the unselected groundselection line GSL2.

After the turn-off voltage VOFF is applied to the second unselectedstring selection line SSL3 or SSL4 and the unselected ground selectionline GSL2, at time T3, first turn-on voltage VON1 is applied to theselected string selection line SSL1 and the first unselected stringselection line SSL2. A first read voltage VR1 is applied to theunselected wordlines, and a second read voltage VR2 is applied to theselected wordline. First turn-on voltage VON1 is applied to the selectedground selection line GSL1, and the turn-off voltage VOFF is applied tothe unselected ground selection line GSL2.

At time T4, an additional operation is performed after a voltage of thefirst unselected string selection line SSL2 reaches a target level offirst turn-on voltage VON1. At time T4, the turn-off voltage VOFF isapplied to the first unselected string selection line SSL2.

FIG. 17 is a diagram of a sixth example of voltages that can be used inthe method of FIG. 3. Compared to FIG. 15, second turn-on voltage VON2is applied to a selected wordline. Afterwards, as illustrated in FIG. 5,first turn-on voltage VON1 is applied to a selected string selectionline, a first read voltage VR1 is applied to unselected wordlines, and aturn-off voltage is applied to an unselected ground selection line.

FIG. 18 is a timing diagram of an example read operation using thevoltages illustrated in FIGS. 5 and 17.

Referring to FIGS. 1 to 3, 5, 17 and 18, at time T1, second turn-onvoltage VON2 is applied to a selected string selection line SSL1, afirst unselected string selection line SSL2, a second unselected stringselection line SSL3 or SSL4, a selected wordline, unselected wordlines,a selected ground selection line GSL1, and an unselected groundselection line GSL2.

After voltages of the second unselected string selection line SSL3 orSSL4, the selected wordline and the unselected ground selection lineGSL2 reach second turn-on voltage VON2, at time T2, turn-off voltageVOFF is applied to the second unselected string selection line SSL3 orSSL4, the selected wordline and the unselected ground selection lineGSL2.

After voltages of the second unselected string selection line SSL3 orSSL4 and the unselected ground selection line GSL2 reach turn-offvoltage VOFF, at time T3, first turn-on voltage VON1 is applied to theselected string selection line SSL1 and the first unselected stringselection line SSL2. A first read voltage VR1 is applied to theunselected wordlines and a second read voltage VR2 is applied to theselected wordline. First turn-on voltage VON1 is applied to the selectedground selection line GSL1, and the turn-off voltage VOFF is applied tothe unselected ground selection line GSL2.

At time T4, an additional operation is performed after a voltage of thefirst unselected string selection line SSL2 reaches a target level offirst turn-on voltage VON1. At time T4, the turn-off voltage VOFF isapplied to the first unselected string selection line SSL2.

In example embodiments, voltage applying methods described withreference to FIGS. 6, 10, 12, 14, and 16 may be a preset operationexecuted at a read operation. The preset operation may be a preparationoperation for performing a read operation on cell strings CS11 to CS41and CS12 to CS42. After the preset operation is performed, a pre-chargevoltage is applied to bitlines BL1 and BL2 and a read operation may beperformed.

In the preset operation, voltages for turning on and off string orground selection transistors may be pre-pulses. The pre-pulses areapplied to prevent phenomenon causing an abnormal operation such as readdisturbance.

Pre-pulses according to embodiments of the inventive concept may bevariously mixed. For example, as described with reference to FIGS. 6,12, 16, and 18, a part of pre-pulses may be set to be lower thanvoltages used at a read operation. As described with reference to FIGS.10 and 14, a part of pre-pulses may be set to have shorter duration ascompared to voltages used at a read operation. Various combinations ofthe lower level and the shorter duration may be made.

FIG. 19 is a circuit diagram of a memory block BLKb according to anembodiment of the inventive concept. Compared to a memory block BLKa ofFIG. 2, a cell string comprises two string selection transistors SSTaand SSTb. In each cell string, string selection transistors SSTa andSSTb may be stacked in a direction perpendicular to a substrate.

In a first row of cell strings CS11 and CS12, string selectiontransistors SSTa are connected in common to a string selection line SSL1a, and string selection transistors SSTb are connected in common to astring selection line SSL1 b. In a second row of cell strings CS21 andCS22, string selection transistors SSTa are connected in common to astring selection line SSL2 a, and string selection transistors SSTb areconnected in common to a string selection line SSL2 b. In a third row ofcell strings CS31 and CS32, string selection transistors SSTa areconnected in common to a string selection line SSL3 a, and stringselection transistors SSTb are connected in common to a string selectionline SSL3 b. In a fourth row of cell strings CS41 and CS42, stringselection transistors SSTa are connected in common to a string selectionline SSL4 a, and string selection transistors SSTb are connected incommon to a string selection line SSL4 b.

A cell string comprises two ground selection transistors GSTa and GSTb.In each cell string, ground selection transistors GSTa and GSTb may bestacked in a direction perpendicular to the substrate. In first andsecond rows of cell strings CS11, CS12, CS21, and CS22, ground selectiontransistors GSTa and GSTb are connected in common to a ground selectionline GSL1. In third and fourth rows of cell strings CS31, CS32, CS41,and CS42, ground selection transistors GSTa and GSTb are connected incommon to a ground selection line GSL2.

In some embodiments, in each cell string, connection between stringselection transistors SSTa and SSTb and string selection lines andconnection between ground selection transistors GSTa and GSTb and groundselection lines may be variously changed or modified. For example, likeconnection between ground selection transistors GSTa and GSTb and groundselection lines GSL1 and GSL2, string selection transistors SSTa andSSTb in a cell string may be connected in common. Alternatively, forexample, like connection between string selection transistors SSTa andSSTb and string selection lines SSL1 to SSL4, string selectiontransistors SSTa and SSTb in a cell string may be connected in common toa string selection line.

FIG. 20 is a block diagram of a memory system 1000 according to anembodiment of inventive concepts.

Referring to FIG. 20, memory system 1000 comprises a nonvolatile memorydevice 1100 and a controller 1200. Nonvolatile memory 1100 may be anonvolatile memory 100 described with reference to FIGS. 1 to 19.Nonvolatile memory 1100 performs a preset operation for applyingpre-pulses as described with reference to FIGS. 1 to 19. Nonvolatilememory 1100 may comprise at least one of nonvolatile memories such as anEEPROM, a flash memory, a PRAM, an RRAM, an FRAM, and so on.

Controller 1200 is connected to nonvolatile memory 1100 and isconfigured to access nonvolatile memory device 1100. For example,controller 1200 may be adapted to control overall operations ofnonvolatile memory 1100 comprising a read operation, a write operation,an erase operation, a background operation, and so on. Controller 1200provides an interface between nonvolatile memory 1100 and a host.Controller 1200 may be configured to drive firmware for controllingnonvolatile memory 1100.

In some embodiments, controller 1200 may comprise features such as aRAM, a processing unit, a host interface, a memory interface, and anerror correction unit. Controller 1200 may communicate with an externaldevice (e.g., a host) according to a particular communication protocol.For example, controller 1200 may communicate with the external devicethrough at least one of various interface protocols such as a universalserial bus (USB) protocol, a multimedia card (MMC) protocol, aperipheral component interconnection (PCI) protocol, a PCI-express(PCI-E) protocol, an advanced technology attachment (ATA) protocol, aserial-ATA protocol, a parallel-ATA protocol, a small computer smallinterface (SCSI) protocol, an enhanced small disk interface (ESDI)protocol, an integrated drive electronics (IDE) protocol, a Firewireprotocol, and so on.

Controller 1200 and nonvolatile memory device 1100 may be integratedinto a single semiconductor device. For example, controller 1200 andnonvolatile memory device 1100 may be integrated into a singlesemiconductor device to form a memory card such as a PC card (PCMCIA,personal computer memory card international association), a compactflash card (CF), a smart media card (SM, SMC), a memory stick, amultimedia card (MMC, RS-MMC, MMCmicro), an SD card (SD, miniSD,microSD, SDHC), a universal flash storage (UFS), and so on.

Controller 1200 and nonvolatile memory device 1100 may be integratedinto a single semiconductor device to form an SSD. The SSD may comprisea storage unit configured to store data in a semiconductor memory. Inthe event that memory system 1000 is used as the SSD, the operatingspeed of the host connected to memory system 1000 may be improved.

As another example, memory system 1000 may be provided as one of variousfeatures of an electronic device such as a computer, a ultra-mobilepersonal computer (UMPC), a workstation, a net-book, a personal digitalassistance (PDA), a portable computer (PC), a web tablet, a wirelessphone, a mobile phone, a smart phone, a smart television, a 3Dtelevision, an e-book, a portable multimedia player (PMP), a portablegame console, a navigation device, a black box, a digital camera, adigital multimedia broadcasting (DMB) player, a digital audio recorder,a digital audio player, a digital picture recorder, a digital pictureplayer, a digital video recorder, a digital video player, a device fortransmitting and receiving information in a wireless environment, one ofvarious electronic devices constituting a home network, one of variouselectronic devices constituting a computer network, one of variouselectronic devices constituting a telematics network, a radio frequencyidentification (RFID) device, and one of various features constituting acomputing system.

Nonvolatile memory device 1100 or memory system 1000 may be packaged invarious kinds of packages. For instance, nonvolatile memory device 1100or memory system 1000 may be implemented with packages such as Packageon Package (PoP), Ball Grid Arrays (BGA), Chip Scale Packages (CSP),Plastic Leaded Chip Carrier (PLCC), Plastic Dual In-line Package (PDIP),Die in Waffle Pack, Die in Wafer Form, Chip On Board (COB), Ceramic DualIn-line Package (CERDIP), Plastic Metric Quad Flat Pack (MQFP), ThinQuad Flat Pack (TQFP), Small Outline Integrated Circuit (SOIC), ShrinkSmall Outline Package (SSOP), Thin Small Outline Package (TSOP), SystemIn Package (SIP), Multi Chip Package (MCP), Wafer-level FabricatedPackage (WFP), and Wafer-level Processed Stack Package (WSP).

FIG. 21 is a block diagram of a memory system 2000 according to anembodiment of the inventive concept.

Referring to FIG. 21, memory system 2000 comprises a nonvolatile memory2100 and a controller 2200. Nonvolatile memory 2100 comprises multiplenonvolatile memory chips, which form multiple groups. Nonvolatile memorychips in each group may be configured to communicate with controller2200 via one common channel. In certain embodiments, the nonvolatilememory chips communicate with controller 2200 via multiple channels CH1to CHk.

In some embodiments, each of the nonvolatile memory chips comprises anonvolatile memory 100 described with reference to FIGS. 1 to 19. Eachof the nonvolatile memory chips performs a preset operation for applyingpre-pulses as described with reference to FIGS. 1 to 19. In the exampleof FIG. 21, one channel is connected to multiple nonvolatile memorychips. However, memory system 2000 can be modified such that one channelis connected to one nonvolatile memory chip.

FIG. 22 is a diagram of a memory card 3000 according to an embodiment ofthe inventive concept.

Referring to FIG. 22, memory card 3000 comprises a nonvolatile memory3100, a controller 3200, and a connector 3300. Nonvolatile memory 3100may be a nonvolatile memory 100 described with reference to FIGS. 1 to19. Nonvolatile memory 3100 may perform a preset operation for applyingpre-pulses as described with reference to FIGS. 1 to 19. Connector 3300may electrically connect memory card 3000 with a host.

Memory card 3000 may be formed of memory cards such as a PC (PCMCIA)card, a CF card, an SM (or, SMC) card, a memory stick, a multimedia card(MMC, RS-MMC, MMCmicro), a security card (SD, miniSD, microSD, SDHC), auniversal flash storage (UFS) device, and the like.

FIG. 23 is a diagram of an SSD 4000 according to an embodiment of theinventive concept.

Referring to FIG. 23, SSD 4000 comprises multiple nonvolatile memories4100, a controller 4200, and a connector 4300. Nonvolatile memory 4100may be a nonvolatile memory 100 described with reference to FIGS. 1 to19. Nonvolatile memory 4100 may perform a preset operation for applyingpre-pulses as described with reference to FIGS. 1 to 19. Connector 4300may connect solid state driver 4000 with a host electrically.

FIG. 24 is a block diagram of a computing device 5000 according to anembodiment of the inventive concept.

Referring to FIG. 24, computing device 5000 comprises a processor 5100,a memory 5200, storage 5300, a modem 5400, and a user interface 5500.

Processor 5100 controls operations of computing device 5000, and it alsoperforms logical operations. Processor 5100 may be formed of asystem-on-chip (SoC). Processor 5100 may be a general purpose processoror an application processor.

Memory 5200 communicates with processor 5100. Memory 5200 may be aworking memory (or, a main memory) of processor 5100 or computing device5000. Memory 5200 may comprise a volatile memory such as a static RAM, adynamic RAM, a synchronous DRAM, or the like or a nonvolatile memorysuch as a flash memory, a PRAM, an MRAM, an RRAM, an FRAM, or the like.

Storage 5300 may be used as a working memory or a long term storagememory of computing system 5000. Storage 300 may comprise a hard diskdrive or a nonvolatile memory such as a flash memory, MRAM, RRAM, anFRAM, PRAM, or the like.

Storage 5300 may be a nonvolatile memory 100 described with reference toFIGS. 1 to 19. Storage 5300 may perform a preset operation for applyingpre-pulses as described with reference to FIGS. 1 to 19.

In various alternative embodiments, memory 5200 and storage 5300 may beformed of a nonvolatile memory of a same type. In this case, memory 5200and storage 5300 may be integrated into a semiconductor integratedcircuit.

Modem 5400 communicates with an external device under control ofprocessor 5100. For example, modem 5400 may communicate with theexternal device in a wire or wireless manner. Modem 5400 typicallycommunicates based on at least one of wireless communications mannerssuch as Long Term Evolution (LTE), WiMax, Global System for Mobilecommunication (GSM), Code Division Multiple Access (CDMA), Bluetooth,Near Field Communication (NFC), WiFi, Radio Frequency Identification(RFID), and so on or wire communications manners such as UniversalSerial Bus (USB), Serial AT Attachment (SATA), Small Computer SmallInterface (SCSI), Firewire, Peripheral Component Interconnection (PCI),and so on.

User interface 5500 may communicate with a user under control ofprocessor 5100. For example, user interface 5500 may comprise user inputinterfaces such as a keyboard, a keypad, a button, a touch panel, atouch screen, a touch pad, a touch ball, a camera, a microphone, agyroscope sensor, a vibration sensor, and so on. User interface 5500 mayfurther comprise user output interfaces such as an LCD, an OLED (OrganicLight Emitting Diode) display device, an AMOLED (Active Matrix OLED)display device, an LED, a speaker, a motor, and so on.

The foregoing is illustrative of embodiments and is not to be construedas limiting thereof. Although a few embodiments have been described,those skilled in the art will readily appreciate that many modificationsare possible in the embodiments without departing from the scope of theinventive concept as defined in the claims.

What is claimed is:
 1. A method of reading data from a nonvolatilememory device, the nonvolatile memory device including a plurality ofcell strings, each cell string including a plurality of memory cells, atleast two selection transistors disposed between the memory cells and abit line, and at least two ground selection transistors disposed betweenthe memory cells and a common source line wherein the memory cells, thestring selection transistors, and the ground selection transistors areserially connected and stacked in a direction perpendicular to asubstrate, the method comprising: performing a preset operation, thepreset operation comprising: applying a first read voltage to a selectedwordline; applying a third read voltage to an unselected wordline;applying a turn-on voltage to string selection transistors of a selectedcell string; applying the turn-on voltage to ground selectiontransistors of the selected cell string; applying the turn-on voltage tostring selection transistors of a unselected cell string; and applyingthe turn-on voltage to at least one of the ground selection transistorsof the unselected cell string; and performing a read operation afterperforming the preset operation, the read operation comprising: applyinga second read voltage to the selected wordline; applying the third readvoltage to the unselected wordline; applying the turn-on voltage to thestring selection transistors of the selected cell string; applying theturn-on voltage to the ground selection transistors of the selected cellstring; applying a turn-off voltage to the string selection transistorsof the unselected cell string; and applying the turn-off voltage to atleast one of the ground selection transistors of the unselected cellstring.
 2. The method of claim 1, where the level of the first readvoltage is equal with the level of the second read voltage and lowerthan the level of the third read voltage.
 3. The method of claim 1,wherein the level of the first read voltage is higher than the level ofthe second read voltage and lower than the level of the third readvoltage.
 4. The method of claim 2 or 3, wherein the level of the thirdread voltage is substantially equal with the level of the turn-onvoltage.
 5. The method of claim 1, wherein the turn-on voltage is apower supply voltage.
 6. The method of claim 1, wherein the selectedcell string and the unselected cell string are connected to the samebitline, the selected cell string being a cell sting including aselected memory cell and the unselected cell string being other than theselected cell string in a memory cell array.
 7. The method of claim 6,wherein the method further includes sensing data delivered to the bitline during the read operation with a sense amplifier.
 8. The method ofclaim 7, wherein the cell strings are arranged on the substrate in rowsand columns, a row of cell strings is connected in common to a stringselection line, and two or more rows of cell strings are connected incommon to a ground selection line.
 9. The method of claim 8, wherein theturn-off voltage is a ground voltage.
 10. A method of reading data froma nonvolatile memory device by performing a preset operation and a readoperation sequentially, the nonvolatile memory device including aplurality of cell strings, each cell string including a plurality ofmemory cells, at least two selection transistors disposed between thememory cells and a bit line, and at least two ground selectiontransistors disposed between the memory cells and a common source linewherein the memory cells, the string selection transistors, and theground selection transistors are serially connected and stacked in adirection perpendicular to a substrate, the method comprising: applyinga first turn-on voltage to string selection transistors of a selectedcell string during the preset operation and the read operation; applyinga second turn-on voltage to one of ground selection transistors of theselected cell string during the preset operation and the read operation;applying the first turn-on voltage to string selection transistors of aunselected cell string during the preset operation and thereafter,applying a turn-off voltage to the string selection transistors of theunselected cell string during the read operation; and applying thesecond turn-on voltage to one of the ground selection transistors of theunselected cell string during the preset operation and thereafter,applying the turn-off voltage to one of the ground selection transistorsof the unselected cell string during the read operation, wherein thefirst turn-on voltage and the second turn-on voltage are different fromeach other.
 11. The method of claim 10, the method further including:applying a first read voltage to a selected wordline during the presetoperation and applying a second read voltage to the selected wordlineduring the read operation; and applying a third read voltage to anunselected wordline during the preset operation and maintaining thethird read voltage during the read operation, wherein the level of thefirst read voltage is equal with the level of the second read voltageand lower than the level of the third read voltage.
 12. The method ofclaim 10, the method further including: applying a first read voltage toa selected wordline during the preset operation and applying a secondread voltage to the selected wordline during the read operation; andapplying a third read voltage to an unselected wordline during thepreset operation and maintaining the third read voltage during the readoperation, wherein the level of the first read voltage is higher thanthe level of the second read voltage and lower than the level of thethird read voltage.
 13. The method of claim 11 or 12, wherein the levelof the third read voltage is substantially equal with the level of thefirst turn-on voltage.
 14. The method of claim 10, wherein the firstturn-on voltage is power supply voltage.
 15. The method of claim 14,wherein the selected cell string and the unselected cell string areconnected to the same bitline, the selected cell string being a cellsting including a selected memory cell and the unselected cell stringbeing other than the selected cell string in a memory cell array. 16.The method of claim 15, wherein the method further includes sensing datadelivered to the bit line during the read operation with a senseamplifier.
 17. The method of claim 16, wherein the cell strings arearranged on the substrate in rows and columns, a row of cell strings isconnected in common to a string selection line, and two or more rows ofcell strings are connected in common to a ground selection line.
 18. Amethod of reading data from a nonvolatile memory device by performing apreset operation and a read operation sequentially, the nonvolatilememory device including a plurality of cell strings, each cell stringincluding a plurality of memory cells, at least two selectiontransistors disposed between the memory cells and a bit line, and atleast two ground selection transistors disposed between the memory cellsand a common source line wherein the memory cells, the string selectiontransistors, and the ground selection transistors are serially connectedand stacked in a direction perpendicular to a substrate, the methodcomprising: applying a first turn-on voltage to string selectiontransistors of a selected cell string during the preset operation andapplying a second turn-on voltage to string selection transistors of aselected cell string during the read operation; applying the firstturn-on voltage to one of ground selection transistors of the selectedcell string during the preset operation and applying the second turn-onvoltage to one of the ground transistors of a selected cell stringduring the read operation; applying the first turn-on voltage to stringselection transistors of a unselected cell string during the presetoperation and thereafter, applying a turn-off voltage to the stringselection transistors of the unselected cell string during the readoperation; and applying the first turn-on voltage to one of the groundselection transistors of the unselected cell string during the presetoperation and thereafter, applying the turn-off voltage to one of theground selection transistors of the unselected cell string during theread operation, wherein the first turn-on voltage is lower than thesecond turn-on voltage.